1. Field of the Invention
This invention relates to fiber-reinforced composite cables.
2. Prior Art
There have already been proposed certain fiber reinforced composite cables or cords in place of conventional steel cables which possess a tensile strength comparable to wire ropes, a smaller thermal expansion coefficient and a lighter weight such as those disclosed for example in Japanese Patent Publication No. 57-25679 and Laid-Open Publication No. 61-28092. Used as reinforcing fibers for such composite cables are glass fiber, aramid fiber and carbon fiber, of which high-strength carbon fiber is reputed for its excellent tensile properties. These reinforcing fibers in actual use have a tensile strength of the order of 300 kg/mm.sup.2 and a tensile modulus of about 23 t/mm.sup.2.
Quality requirements of late grow more and more strict for fiber-reinforced cables not only with respect to weight, corrosion resistance and thermal expansion, but also to tensile modulus exceeding that of steel. To achieve sufficient moduli with composite cables containing about 60 vol. % of reinforcing fibers, it would be necessary to use a fibrous material which has for itself a modulus of at least 35 t/mm.sup.2 or somewhat greater than steel's modulus of about 20 t/mm.sup.2. It would appear that good fiber-reinforced composite cables can be made available with such high tensile moduli. However, it has now been found that high modulus parameter alone fails to produce a truly satisfactory composite cable capable of demonstrating a full performance of reinforcing fibers per se as hereafter described.